1. Field of the Invention
The present invention relates to a resin film forming method, to a laminate production method and apparatus and in particular to an art of suppressing a neck-in phenomenon or the like in extruding a resin from an extruder die to form a resin film and inhibiting the occurrence of craters on a resin film surface of a laminate.
2. Description of the Related Art
Generally on extruding a resin from a extruder die to form a resin film and producing a film-shaped product from this resin film or a film-shaped stack obtained by laminating or coating the resin film onto a support, a phenomenon known as so-called neck-in occurs, in which the extruded film has a width smaller than the extruding width. It is accompanied with a problem that the film thickness at both ends in width direction of the resin film becomes greater than that at the center. Furthermore, in case of forming a resin film at high speed owing to the speedup of production line, there is also a problem that a phenomenon of film shake takes place owing to the unstable both ends in width direction of the resin film and the film width is not kept constant, thereby decreasing the yield. In this case, a technique of resin edge stacking in width direction is present principally for purposes of recycling-up, but there is a problem that a film is separated between the central resin and the marginal resin of the resin film at the time of edge stacking of resins different in physical property.
Namely, in forming of a resin film by using an extruder die, there are principally (1) a problem of neck-in and its accompanying increase in thickness at both resin ends, (2) a problem of film shake and (3) a problem of film separation originating from the difference of resin in physical property between the center and both ends of a resin film and thus measures to improve these have been desired. These problems are not limited to the case of extruding a resin from an extruder die but take place also in case of ejecting a coat liquid from an extruder die.
So far, as countermeasures against the above problems, there have been adopted a method for improving the material physical property by mixing a plurality of materials (Japanese Patent Publication Nos. 64-3655 and 5-82806), a method of changing the flow of a resin in the extruder die (Japanese Patent Publication No. 6-61819 and Japanese Patent Application Publication No. 64-64822) and a method of cooling both ends of the resin film extruded from an extruder die (Japanese Patent Publication No. 5-33134).
However, the method for improving the material physical property has a drawback of deficiency in general usability because a suitable additive must be added for each material. The method of changing the flow of a resin in the extruder die by using a forming plate has a drawback of being ineffective for the film shake though effective for the suppression of neck-in. The method of cooling both ends of the resin film extruded from an extruder die has a drawback that no stable effect can be obtained in case of an increase in line speed.
Widely adopted in the production of a laminate such as support for photo printing paper is an extrusion laminate method (also referred to as an extrusion coating method) of laminating a resin film on a support by not only coating but also nipping a resin film of a thermoplastic resin such as polyolefin extruded from an extruder die to a running support for pressure adhesion at the nip point between a nip roller and a cooling roller.
In the production of this laminate, minute pores (hereinafter, referred to as craters) may appear on the surface of the resin film laminated on a support. When the number of these craters is great, the outer appearance of a product is damaged, and the glossy feeling also lowers in the case of the laminate being used as a photoprint paper support, for example, so that the product markedly decreases in value. The occurrence of craters is attributable to the fact that the accompanying air is, under influence of the accompanying air generated on the rotation of a cooling roller, accumulated in the area between the resin film and the cooling roller and a convex recess arises on the resin film. With increasing line speed in the production of a laminate, with decreasing thickness of the resin film, with lowering discharge temperature of a resin from the extruder die, with smaller nip pressure and with greater surface roughness of a support, craters become more likely to occur.
As preventive measures against the occurrence of craters, various examinations have been made, for example, from the viewpoint of a resin like Japanese Patent Application Publication No. 8-36238, from the viewpoint of an improvement in the surface of a support like Japanese Patent Application Publication No. 4-81836, on the basis of specifying the process conditions like Japanese Patent Application Publication No. 6-214342 and on the basis of proposing a new equipment for spraying a gas permeable through a resin film toward the nip point like Japanese Patent Application Publication No. 63-246227.
Though effective in its own way, however, the above-mentioned preventive measures against the occurrence of craters involved a problem that no sufficient effect could be obtained in case of a line speed rise in the production of a laminate.
In this case, the provision of a windshield plate has been proposed as a further improvement of the equipment in Japanese Patent Application Publication No. 63-246227, but is not fully effective in case of speedup to a high speed range equal to or greater than 300 m/min and a contact of the windshield plate with a cooling roller brings about a fear of damaging the cooling roller.